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Nov. l2, 1946.
1_. A. MEACHAM '
Filed NOV. 16, 1945
Patented Nov. 12, 1946
Lamed A. Meacham, Summit, N. J., assignor to
Bell Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
Application November 16, 1943, Serial No. 510,481
6 Claims.
This invention relates to call transmitters and
more particularly to key-controlled transmitters
which are .adapted to generate alternating cur
rent key signal impulses that may be utilized in
one speciñc use, to indicate telephone station
>At the present time, telephone systems which
operate on the basis of keyed alternating current
signals are systems in which the signals them
selves, when indicating a wanted telephone num
ber, are impulses comprising Coded combinations
ofirequencies, preferably within the voice fre
quency range, and these impulses are produced
either by an alternating current generator hav
ing a number` of reeds which can be simultane
ously plucked in the required combination by a
digit-designating key to induce the wanted fre
quencies in a pick-up coil interlinked with a mag
netic ñeld, or by the permutative application to
the line of the required number of generators
each individual to one of the frequencies. At the
remote end of the line these frequencies are re
ceived by suitable frequency-responding appara
(Cl. 179-90)
tus ordinarily necessary for response to the in
coming signal frequencies, for instance, if econo
mies could be effected in the channels which re
spond to the indivdual frequencies, As already
intimated, these channels are fairly expensive
due to the necessity of providing for each chan
complex iilter network, an amplifier, a rec
tifier, a sensitive relay and, further, additional
equipment to protect the channels against false
response to noise induced currents.
To the end of simplifying and reducing the
quantity of central oflice equipment necessary for
key pulsing and thus provide more efûcient tele
phone service, I have devised a telephone sys
tem covered :by my copending application Serial
No. 510,482, filed November 16, 1943, now Patent
No. 2,396,111, granted March 5, 1946, which op
erates on “polarized” signals; that is, a telephone
system in which the designation of the wanted
line consists Aentirely of a coded succession of
spaced positive and negative lobes of an alter
nativel current.
I_n other words, the impulses
that comprise the wanted designation do not con
tus which, in the most general case, comprises
sist of a train of alternations of mixed or single
a channel for each frequency that includes a 25 frequencies persisting on the line for a given
filter network tuned to the frequency to be passed,
period, ‘but only of a number of single alterna
an ampliñer, a rectiñer for changing the ampli
tions or single full cycles, the ñrst half of each
lied frequency into a direct current, and a sensi
cycle denoting the coded indication of the pulse.
tive relay to operate in response to that current,
` The present invention has to do with a call
the momentary operation of the latter usually 30 transmitter intended for use with the invention
being registered in the storage devices of a
covered by the above-mentioned copending ap
switching control mechanism called the “sender”
plication or, for that matter, with any other` in
which, in response to the registration, subse
vention or device in which polarized impulses are
quently controls the selective positioning of the
utilized, and the object of the present invention
switches to connect with the Wanted line.
is a call transmitter capable of generating polar
Telephone systems operating on alternating
ized impulses of` the type described which is sim
current impulses have a number of advantages
ple and reliable to operate, compact in structure
over those which operate on direct current im
and economical to produce.
pulses. For example, they permit a longer “dial
More specifically, the invention, in one embodi
ing” range and are faster than the dial operated 40
herein described by Way of illustration,
system because the closure period of the required
comprises an electro-mechanical device in which
number o_f keys, each of practically equal dura
tion, is less, on the average, than the correspond
the depression of a numerical key causes a cam
of high permeability to move rapidly through a
ing operating period of the dial for producing
magnetic ñeld. The 'edge of each cam is so
the equivalent trains of pulses that indicate the 45 shaped as to vary the reluctance of the ñeld
same designation. These >advantages make for
and thus generate the desired series of single
the more rapid establishment of telephone con
nections with consequent beneiits to the public
which receives more rapid service and to the
cycle pulses in a suitable coil interlinked With
the magnetic ñeld. On release of the key, the
cam is restored more slowly to its normal posi
operating company which can render the service 50 tion so that, as the cam returns, substantial
with less apparatus.
change of magnetic reluctance is avoided and
Key' pulsing (as alternating current pulsing is
the production of any detectable pulses is pre
most usually termed) would be productive of
even greater saving if it were possible to simplify
Other features and advantages of the inven
and reduce the quantity of central oilice appara 55 tion will appear from the following description
and the claims appended thereto, reference be
ing had to the accompanying drawing in which:
Fig. 1 shows a plan View of the device with
the key plate partly removed to show the in
terior arrangement of parts;
Fig. 2 shows a side elevation of the device
along the section line 2_2 of Figi;
Fig. 3 shows the key detail viewed from the
left of Fig. 2, with the key in the normal posi
and the latter extends clear through the hole to
the under surface of the box, the nut Z‘Ll being
threaded upon the bolt to engage the sleeve,
which is thereby tightened against the collector
ring 9 by an appropriate lnumber of turns of
the nut 2G.
The magnet 8 is, as said before, a cup-shaped
structure invertedly secured underneath the
plate 20. This magnet is formed with ten equi
10 spaced narrow vertical slots through each of
which an arcuately shaped cam 3 of high per
Fig. 4 is an isometric View of the magnet and
meability is adapted freely to pass and move
pick-up coil assembly with two of the ten mov
therewithin in a vertical plane, and each of the
able cams shown in a normal position by way of
.cams is so mounted upon the tcp plate of the
illustration, the other cams having been omitted
to show more clearly the construction of the 15 box lli as hereinafter set forth that, in its nor
mal position, its edge is substantially in align
ment with the rim of the collector ring 9. Each
Fig. 5 shows a curve of the‘wave form which
cam `has an upturned vane i2 and the periphery
may be produced by the device.
of the cam is formed with four equally spaced
Referring to the various ñgures of the draw
ing in which identical designations in the differ 20 indentations and projections H, which are per
mutatively disposed thereon according to a code
entñgures refer to identical parts, 1 is the re
of four single alternating current cycles, each
ceptacle or container which, preferably, may be
combination of which indicates one of the ten
round »and dimensioned to fit the space in the
telephone instrument which is provided for the
To the upper surface of the box i6 there is
conventional impulse dial. 'I'he top or key plate
secured or otherwise provided in any suitable
29' is provided with ten equispaced holes ra
manner ten radially disposed ears Íi8 upon each
dially disposed around the plate, Aand in each
of which is mounted one of the cams 3, the
hole is inserted a key .l Iwhose shank i1, the
latter being freely supported upon the ear by
lower portion. of which .is bifurcated, slidably
means of a pin i9. Each ear is so located around
passes therethrough. Each key is surmounted 30 the
upper surface of thetop'plate .of the box
with a designating button containing the letters
and the >numeral usually found in the corre
sponding ñnger holes of the ordinary telephone
that,_with the cam 3 located on the outer `ex-k
tremity of the pin i9 (see Fig. 3), the
positioned directly opposite a slot in the magnet
dial, and each key can be moved up and down
inthe receptacle 'I by pressing upon the button 35 8. A coiled spring 6 is wound around the shank
of the pin and anchored, on the one end, to a
thereof.'> At the bottom of the receptacle is
hole in the ear and, on the >other end, Vto the
placed a box-like structure i4 the top plate oi
camrnear the left edge thereof. The spring is
which, among other things, is provided with
so 'as to provide tension normally tourge
holes which arealigned with and equal in di
to rotate withinthe slot, but the cam
mension tocorresponding holes in the key plate
is maintained against the spring tension and
2l).VA The shank of each key is long enough to
in its normal position with its- lower edge in
alignment with the rim ofthe collector .ring 9
a portion of ' the shank normally protruding
by the ratchet spring Il latched inthe escape
below» the' top plate thereof, thus providing the
key with aligned vertical supports at two points 45 ment detent formed at the bottomof .the cam.
The spring il, of which one is provided for each
to insure its unswerving vertical movement on
cam, is secured to the top of the box i4, each
depression and release. The depth» of the box
spring being positioned with respect to its cam
i4 >is such, ofV4 course, as to provide, on the :full
normally to lengage the escapement detent
depression Vof the key, full clearance between
the end _of the shank and the bottom of the box. 50 thereof. Opposite the end of each cam on the
top plate of box lâ is a slot (not shown) which
The upward movement of the key is limited by
is Wide enough to allow the free passage there
the stop I3 which, as the key moves upwardsV
through of the cam when the latter is'. rotated
inthe manner shortly to be described, catches
in the manner shortly to be described. Thus
the under surface of the plate 28 and brings the
pass through the aligned hole vin the box i4 with
key >to rest.
'Y Fitted into the receptacle 1 is thel electro
magnetic structure of the device. This struc
ture comprises a hollow, inverted, cup-shaped
permanent magnet 3 within which is ñtted the
hollow iron core 2'! having the coil l0 mounted
thereon andthe whole assembly secured tothe
bottom of the plate 20 by means of the mag
netic bolt 22 which passes through aligned holes
in the center of the plate 20, the center of they
magnet 18 and the center of the box lli, said bolt
being force fitted through the core. >To the
lower'end of the coil spoolhead is secured the
magnetic collector ring 9 which is held >tightly
againstV vthe spoolhead by the nut `2li threaded
upon the 'lower end of the bolt 22 and screwed
tightly 1 against the non-magnetic sleeve 23
which is mounted upon that portion of the bolt
22 that extends below the collector ring 9. The
central hole in the box i4 is made wide enough
permit the passage of the sleeve 23 therethrough
55 when ’a cam is rotated so that that portion-of
its periphery which lies outside of the magnet
8 is brought within the magnet so that its op
posite extremity is practically in line with the
rim of the collector ring 9 (as shown, for ex
60 ample, by the right cam in Fig. 2) a portion of
the cam passes through the slot provided _there
for in the top plate of box I4 into the Well below
Each cam 3 is actuated by one- of the keys IV.
65 As previously stated,l the lower portion of the
shank l1 of each key is bifurcated, the left fork
having a weak spring -2 _coiled therearound with :
its upper end abuttingagainst the juncture of the .
y Atwo forks and the lower end~ resting upon- the
70 upper plate of the box lli. The_right forkhas a
horizontal projection 5 which normally rests Aun
derneath the vane l?. of the cam. `
. It
" .
will be
observed that, with- the
was 3 i111
their-‘normal position, as indicated, forrexample, .
75 by the left -cam in Fig. 2, there isa small air-gap
between the edge of the collector ring 9 and the
spring 2 is weak and the mass of the key great
relative to that of the cam, the key and the cam
will restore very slowly as compared with the rapid
bottom end of the cam. Now when the cam is
rotated so as to fully enter the magnet slot as
movement of the cam on operation. Since the
more particularly described hereinafter, this air
gap is increased when an indentation on the pe 5 production of the alternating potential is a func- .
riphery of the cam passes the edge of the ring
tion of the time rate of change in the reluctance of
and is decreased when a projection passes the
the magnetic circuit, the slow rate at which the
edge of the ring. The reluctance of the mag
cam returns to normal will produce llIlaDDl‘eCî
netic circuit formed by the magnet 8 and the core
able changes in the reluctance of the circuit as
2l through the intermediary of the rotating cam
the projections and indentations on the periph
3 thus increases in the case of an indentation and
ery of the cam 3y pass by the rim of the collector
decreases in the case of a projection, thereby
ring 9. No pulses identiñable as such will thus be
causing a decrease in the strength of themag
produced on the return of the cam.
netic ñeld in the former case and an increase in
It is desirable that the angular velocity of the
the latter case. For the brief interval during
cam 3 be approximately constant while pulses are
which an indentation l! rapidly passes the edge
being generated so that they may be uniform in
of the ring 9, the magnetic held is varied from
amplitude and spacing. The cams should, there
its normal strength at the time that the unin
fore, be arranged to be accelerated to their max
dented surface of the cam is opposite the edge of
imum velocity in the interval before the first
the ring to a minimum strength when the great
pulse is produced. The “maximum velocity”
est depth of the indentation is opposite the edge
may be maintained by the limiting action of the
of the ring and back again to normal strength
vane l2 projecting from the cam which provides
when the unindented edge of the cam is again
suitable wind resistance.
opposite the edge of the ring. This will have the
While I have described my invention in con
effect of inducing in the coil lil (which may be 25 nection with one speciñc embodiment thereof,
assumed to be part of a closed electric circuit) a
it is to be understood that various other applica
single cycle of alternating potential the ñrst lobe
tions and embodiments thereof may be made by
of which is negative and the second lobe is posi
those skilled in the art without departing from
tive. On the other hand, for the brief interval
the spirit of the invention as deñned within the
during which a projection rapidly passes past the -
edge of the ring, the reluctance of the magnetic
circuit is decreased and the magnetic ñeld there
through will vary from normal to a maximum
when the highest point of the projection is near
est the edge of the ring and back to normal when
; scope of the appended claims.
What is claimed is:
l. A device for generating a polarized pulse
comprising a magnetic circuit, a coil magnetically
coupled to the lines of force of said circuit, and
a controllable magnetic member for momentarily
the projection is well past the edge of the ring,
thus giving rise in the coil lli to a single cycle of
alternating potential which is of opposite polarity
varying the reluctance of said circuit whereby
that will be produced by the rotation of a cam is
magnet, a pick-up coil mounted upon said mag
net, a plurality of keys and means operated by
said variation induces in said coil a single full
wave alternating potential.
to that produced` by the indentation. A Curve
2. A generator for the production of predeter
illustrative of the type oi potential alternation 40 mined polarized electric impulses comprising a
indicated in Fig. 5, which shows three positively
polarized pulses followed by a negatively polar
each of said keys for varying the field of said
ized pulse produced by a cam (not shown) hav
magnet in accordance with the polarity of the
ing three projections followed by an indentation. 45 impulses to be produced, whereby an increase in
Having described the various mechanical ele
the intensitl7 of said ñeld caused by said means
ments of the device together with their arrange
induces an electromotive force in one direction in
ment and interrelation, I will now describe the
said coil and a decrease of said ñeld caused by
manner in which the device operates.
said means induces an electromotive force in the
When a key l is depressed against the pressure
opposite direction in said coil.
of its spring 2, the associated magnet Cam 3 does
3. A generator for the production of predeter
not move immediately, for the latter is held in
mined polarized electric impulses comprising a
magnet, a pick-up coil mounted upon said mag
place by the ratchet spring 4. However, as the
key l approaches the bottom of its stroke, the
net, a plurality of keys, and a plurality of means
projection 5 of the key strikes against the ratchet
each respectively operated by one of said keys
spring 4 and disengages the latter from the de
for momentarily varying the ñeld of said magnet
tent on the cam, allowing the cam to be rotated
as many times as there are impulses to be pro
rapidly by virtue of the tension in spring 6 to
duced, whereby an increase in the intensity of
the position illustrated by the cam 3 at the right
said iield caused by one of 'said key-operated
in Fig. 2. As the cam rotates and its projections 60 means induces an electromotive force in one di
and indentations ll pass rapidly by the edge of
rection in said coil and a decrease in the intensity
the collector ring 9, single cycles of alternating
of said field caused by one of said key-operated
voltages of the type indicated in Fig. 5 are in
means induces an electromotive force in the oppo
duced in the coil ll'l. The motion of cam 3 is
site direction in said coil.
stopped when its vane I2 strikes the top of the 65 4. A generator for the production of predeter
projection 5.
mined polarized electric impulses comprising a
When the pressure is removed from the de
magnetic circuit including a stationary magnet
pressed key I, the tension stored in spring 2
and a plurality of magnetic elements disposed in
causes the key to be restored. In its upward
proximity of said magnet to provide a normal
movement, the projection E of the key engages
reluctance for said magnetic circuit, means for
the vane l2 of the cam and while the key is
moving any one of said elements in relation to
raised the cam is turned counter-clockwise about
said magnet for momentarily increasing or de
the pin I9, reaching its normal position by the
creasing said reluctance permutatively a prede
time the dog i3 engages the under surface of the
termined number of times equal to the number
plate 20 and thus brings the key to rest. Since 75 of impulses to be produced, and a pick-up coil in
terlinked with said magnetic circuit whereby the
6. A generator for the production of equally
increase in the reluctance of said circuit caused
spaced polarized electric impulses comprising a
by the movement of any one of said magnetic ele
magnetic circuit including an inverted cup-shaped
ments induces an electro-motive force in one di
magnet having vertical slots radially and equally
rection in said coil and the decrease induces an Ul spaced thereon, a core interiorly affixed to the
electromotive force in the other direction in said
~ 5. A generator for the production of predeter
center of said magnet, said core having a collector
ring at the base thereof, and a pluralityrof arcu
ate magnetic cams each having on its periphery
mined-polarized electric impulses comprising a
equally spaced projections and indentations per
magnetic circuit including an inverted cup-shaped 10 mutatively arranged thereon according to a pre
magnet having vertical slots radially and equally
determined code, the total of such projections and
spaced thereon, a core interiorly alîlxed to the
indentations being the same for each cam, each of
center of said magnet, and a plurality of arcuate
said cams being positioned for rotatable uniform
magnetic cams each having on its periphery pro
movement within a slot in said magnet at a dis
jections and indentations permutatively arranged 15 tance from the collector ring to provide an air
thereon according to a predetermined code, the
gap between said collector ring and the periphery
total of such projections and indentations being
of the cam which upon the rotation of the cam
the same for each cam, each of said cams being
shall be increased by an indentation and de
positioned for rotatable movement within a slot
in said magnet at a distance from the core to pro 20 creased by a projection to thereby momentarily
increase and decrease, respectively, the reluctance
vide a normal air-gap between the core andthe
of 'said magnetic circuit, and a pick-up coil
periphery of the cam which shall be increased by
mounted upon said core- to interlink said mag
an indentation and decreased by a projection to
netic circuit whereby the increase in the reluc
thereby momentarily increase and decrease, re
spectively, the reluctance of said magnet circuit, 25 tance of said circuit induces `an electromotive
and a pick-up coil mounted upon said core to
interlink' said magnetic circuit whereby the in
crease in the reluctance of 'said circuit induces
an electromotive force in one direction in said
coil and the decrease induces an electromotive 30
force in the other direction.
force in one direction in said coil and the decrease
induces an electromotive force in the other di
rection in said coil.
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